Recently, techniques for treating waste resin materials such as waste polystyrene resin and polystyrene foam, having an apparent volume larger than the actual solid (resin component) volume, have been developed (see, for example, Japanese Patent Application Laid-Open (kokai) Nos. 2-1748, 5-59212, 7-113089, 9-40802, and 9-157435, 2001-181439). According to these techniques, waste resin material is brought into contact with a solvent to form a gel, whereby the volume of the waste resin material is reduced to a volume almost equivalent to the actual volume. Then, the resin is separated from the solvent and reused as a fuel or a resin raw material, while the solvent is reused as a solvent for the volume reduction treatment.
In one procedure proposed in the above, relatively new technical field, resin (solid) and solvent (liquid) are separated from a gel product through evaporation of the solvent to thereby yield a solid, and condensing the vapor to recover the solvent. Generally, the treatment in which waste resin material is brought into contact with a solvent to form a gel, whereby the volume of the waste resin material is reduced to a volume almost equivalent to the actual volume, is referred to as volume-reduction gelling or simply as volume reduction. The resin that has been gelled to gelatinous solid or gel is called volume-reduced gel-state polystyrene resin. Two methods have been proposed for separating resin and solvent from volume-reduced gel-state polystyrene resin. One method includes evaporating solvent of the volume-reduced gel-state polystyrene resin, and the other method includes pressing the volume-reduced gel-state polystyrene resin to thereby separate the solvent. In the latter method, a very small amount of solvent remains in the resin, and the solvent is further evaporated in accordance with needs.
In general, liquid (solvent) is evaporated by heating the liquid (solvent), and the liquid (solvent) is recovered by condensing the vapor thereof. Similarly, solvent contained-in-volume-reduced gel-state polystyrene resin or in a resin that is produced by removing solvent through pressing from volume-reduced gel-state polystyrene resin is evaporated through heating.
Japanese Patent Application Laid-Open (kokai) No. 2001-181439 discloses a polystyrene-recovering apparatus including a dissolving tank for forming a liquid by adding a solvent to a gel containing polystyrene in solvent; a filter for filtering the liquid; a condenser for evaporating the solvent contained in the liquid that has passed through the filter, thereby forming a concentrate-having a predetermined concentration; and a separator for evaporating the solvent contained in the concentrate, thereby recovering polystyrene. The separator of the apparatus is a thin-layer-evaporation separator 90 composed of a double vessel including a separator inner cylinder 91 and a separator outer cylinder 92. In the separator, a heating medium for heating is circulated in the space between the inner cylinder 91 and the outer cylinder 92, and the concentrate is supplied through the inner cylinder 92. In this case, the concentrate flows down through the inner cylinder 92 while the solvent contained in the concentrate is gradually evaporated. In order to ensure smooth flow which would otherwise be prevented by an increase in resin concentration, a plurality of scraping plates 97 are provided surrounding a rotation axis 95 by the mediation of rotation arms 96 so that the resin adhering on the inner cylinder 92 is scraped.
However, the aforementioned conventional resin/solvent separator, which, by heating, evaporates the solvent contained in volume-reduced gel-state polystyrene resin fed to the apparatus main unit and flowing down in the apparatus, attains poor solvent removal efficiency, raising the problem that the solvent is not sufficiently removed, resulting in poor treatment efficiency. In addition, resin quality after removal of solvent is unsatisfactory. When such resin is extruded to form pellets, undesired cutting occurs due to air bubbles remaining in the resin, which is problematic.
Japanese Patent Application Laid-Open (kokai) No. 2001-310971 discloses an apparatus for separating and recovering styrene and ester-based vegetable oil from a mixture containing volume-reduced water styrene foam and ester-based vegetable oil. The apparatus has a double-wall cylindrical tank 11 which can be maintained at a predetermined temperature and which includes therein a plurality of stages of warming beds 12 in the vertical direction for maintaining the temperature equivalent to the temperature inside the cylindrical tank 11. Each warming bed contains concentrically arranged warming pipes 121 at small intervals. In the apparatus, when the above mixture is spouted out onto the uppermost warming bed 12 of the warming beds 12 provided in the vertical direction, the mixture is then spouted out by means of a roller 131 from the cavity among the warming pipes 121 onto the warming pipes 121 of the subsequent warming bed 12. Since the mixture is heated through the warming pipes 121, ester-based vegetable oil is evaporated. Through repetition of the above process, the mixture is separated into the ester-based vegetable oil and waste styrene foam.
Through employment of the above apparatus, the mixture can be relatively sufficiently separated into resin and solvent. However, since the ester-based vegetable oil and waste styrene foam is obtained from the mixture by subjecting the mixture to the heating step a plurality of times, the separation operation becomes cumbersome and requires a long period of time, thereby lowering operation efficiency, which is problematic.